Hollow stems don’t mean the plant is weak, in any way. Plants that are hollow between internodes are quite strong, much like bamboo, and normally grow into the tallest plants with the largest flowers. These plants can hold a lot of weight without breaking.
Back in the ‘70’s, I used to hear my uncle and his friends talk about the correlation between hollow stems and really good weed. They also talked about breeding regular cannabis plants with hemp for various reasons.
One of my mentors for learning to grow cannabis was a master gardener and he told me that hollow stems in cannabis came from hemp plants and people have been breeding drug cannabis plants with non-drug hemp plants for generations. He said the crossings were done to create new flavor profiles, among other things like improved structure and vigor.